The answer is to press STOP-N while booting restores the default NVRAM
settings. My problem was the orig sun keyboard I tried to use was out
of order ;-(
I took another one, did the trick, and it worked.

Thanks again & best wishes,
Guenter

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My orig question was:
> accidentially the contents of the NVRAM values of an Ultra Enterprise 450
> server was lost. Also the settings for a serial console (old DEC VT220).
> Console settings are 9600,8,n,1 on Serial Port A. The Serial Ports are
> configured to RS-232, not RS-423.
> If I try to boot I only get one confusing line of Characters on my VT220
> ("ZZSSSIx.........") but no OBP prompt.
> Is it possible to restore the factory defaults of the NVRAM chip?